This invention relates to illumination schemes for image capturing devices, particularly devices for obtaining an image of a surface which has coded or alphanumeric information affixed thereon.
Image capturing devices are desirable in the package delivery field, where in-transit parcels bear labels having bar codes printed thereon containing customer shipping information. It would be desirable to obtain images of these labels from the surface of such in-transit parcels. The image of the label would desirably be electronically transmitted to a data processing apparatus where the customer shipping information is retrieved, expediting handling and delivery of the parcel. Retrieval of the shipping information depends heavily on the ability of the image capturing device to obtain a complete and accurate image of the bar code or label affixed to the parcel's surface. Improper lighting, glare and shadows can all reduce the quality of the image obtained and impair the ability to retrieve the shipping information.
To improve image quality, hand-held image capturing devices have been proposed that incorporate some type of internal illumination scheme. The goal of these illumination schemes is to enhance image retrieval by providing controlled illumination to the surface to be imaged, thereby ensuring that the image of the bar code or label obtained is readable by the data processing apparatus. These devices, however, fail to provide readable images because the lighting schemes employed do not produce uniform illumination across the entire surface to be imaged. Frequently, these schemes illuminate certain portions of the surface too intensely, creating "hot spots." When light reflected from such a "hot spot" is focused on a CCD chip, for example, CCD elements will receive more light than their capacity, obliterating or distorting the image of the label or bar code produced by the CCD chip. Alternatively, certain portions of the surface, especially the corners of the bar code or label, may receive light which is insufficient to cause CCD elements to respond, thus creating an image with "shadows." These "shadows" prevent the data processing means from retrieving the customer shipping information from that portion of the image subject to the "shadow." Even if the surface to be imaged is illuminated without severe "hot spots" or "shadows," the difference in distinguishing between the various levels of illumination produced at that surface by these devices needlessly complicates signal processing.
These drawbacks represent a particular problem in obtaining information from a label having a two-dimensional symbology or an alphanumeric label. Such labels typically lack the redundancy present in bar codes. Consequently, information is lost when any portion of the label is improperly illuminated.
An example of this type of illumination scheme is U.S. Pat. No. 5,032,960 entitled "Light Source Device With Arrayed Light Emitting Elements and Manufacturing Therefor," issued to Katoh on Jul. 16, 1991. The Katoh patent discloses a series of light-emitting diodes ("LEDs") arranged linearly on a printed circuit board which, in conjunction with a convergent lens, provides illumination along a line, thus permitting scanning across a surface. It is intended for use in an imaging device such as a copier. The time required for imaging using the device taught in Katoh is accordingly excessive when compared with the requirements of parcel processing.
Accordingly, it is an object of this invention to provide an LED illumination scheme that provides simultaneous uniform illumination across the entire surface of an object to be imaged or scanned.
Further objects and advantages of the invention will become apparent from the detailed description of a preferred embodiment set forth below.